1. Field Of The Invention
The present invention relates primarily to processes for the recovery or removal of metal values from aqueous media. The present invention further relates to environmental clean-up while the process finds particular but not necessarily exclusive utility in the recovery of metal values from aqueous media, it is useful as well for the removal of contaminants from soil and the like and for the removal of metal values or other contaminants from water.
2. Description Of The Prior Art
Fathi, Habashi, "Principles of Extracting Metallurgy". Vol. 2. "Hydrometallurgy". Gordon & Breach Science Publishers, 1970, review some of the hydrometallurgy art relating to the processes of this invention Chapters 1, 2 and 15. Hydrometallurgy includes a variety of unit processes useful in the recovery of metals from ores. Flotation and ion flotation utilize a surface active agent and a gas to separate free metal, ions and/or metal compounds from gangue. The surface active agent adheres to at least one of the solid particles in a slurry and to rising air bubbles thereby lifting the adhered metal, ion, metal compounds, or gangue particles to the surface. Thus, flotation is utilized in the recovery of metal by collecting particles ranging from ions to suspended free metal particles. A sequence of extractive steps using different surfactive agents can separate out a series of metals or ions.
Surface active agents can range from detergent ions, e.g., sodium lauryl sulfonate, to polymers having molecular weights in the millions, e.g., polymeric sulfonates. The specific surface active agent(s), process steps and conditions depend, among other things, on the "water" or "oil" wetting character of the ion(s), metal(s), metal compound(s), gangue, etc. Many of the physical and chemical mechanisms used in flotation are also operative in collecting metals, etc. using flocculation. Many flocculating agents are high molecular weight polymers, such as polyacrylic acids and/or polyacrylamides. (See R. L. Davidson, "Handbook of Water-Soluble Gums and Resins". McGraw-Hill Book Co. 1980, Chapters 16 and 170.) The materials flocculated range from suspensions or solutions of charged solutes to free metal particles. To accomplish these results, specific surface active agents are utilized with particular metals, etc. under specific process conditions.
In leaching, a solvent is used to solubilize and extract a soluble constituent from an ore, ore concentrate, industrial waste, etc. The processes can be simple or more complex. In a simple process, an ore body may be shattered and leached in place or comminuted ore may be piled on a paid or dumped into a tank prior to leaching. Gold and other precious metal particles are sometimes entrained in the leaching step and provide a mixed recovery of metal ions and metal particles. The more rigorous leaching processes use concentrated solvent, high temperatures, high aerobic or anaerobic gas pressure, etc., and can be dangerous. Some of the processes are also multistep and require a series of treatments.
The physical and chemical forces actuating the summarized collection procedures vary with the specific collection system. They may include one or more of hydrogen and/or covalent bonding, electrostatic forces, molecular sieving, van der Waal's forces, etc. Collection by ion exchange, however, is usually based on only a chemical exchange.
Ion exchange resins are always relatively rigid due to a high degree of crosslinking and the attachment of the ionic substituents to, e.g., a styrene backbone. Because of this rigidity, there is much less ion exchange capacity and hydration of the fixed ions within the resins. The resins are typically manufactured so that they can only imbibe from about 23% to about 264% water. Sometimes, special steps can be taken to increase the internal porosity of the particles in order to fully use the fixed active ion capacity. The rigidity created by the increased crosslinking is, however, a benefit because the ion exchange resins must be resistant to degration resulting from handling, movement within the bed or column and osmotic shock. Ion exchange resins sometimes are said to be in the "gel" form, although the "gels" are significantly different in their physical and chemical properties than those of the hydrogels.
Hydrated hydrogels are quite flexible polyelectrolytes which are not based on a styrene or similarly rigid backbone polymer like the resins and have a much greater number of available fixed ions. They can take up enormous volumes of water, e.g., up to 1200 times their weight, but are more easily degraded physically.
Both the resins and hydrogels have many uses. While the primary use of ion exchange resins is in water softening and other chemical processing (including metal purification), hydrogels are used in many fields ranging from contact lens eye glasses to agricultural additives. In special forms they have even been generally taught to be useful in metal recovery. See Robert Steckler, U.S. Pat. Nos. 4,036,778; 4,058,491; 4,060,678; 4,071,508 and 4,163,092. These patents teach complex copolymer combinations of polyacrylates, polyamides and other polymers which have moieties enabling them to be strong or weak acid or strong or weak base complexers or reactors with metals, and a variety of other materials. These hydrogels only take up to about 100% water, by weight. Effectively, Steckler teaches ion exchangers.
U.S. Pat. No. 4,402,725 issued to H. Heller et al teaches the embedding of ion exchangers into hydrogels to create fertilizers and the additional of a coated magnesium sulfate material to the mixture.
Japanese Patent 80/127,143 issued to Japan Kokai Tokkyo Koho (Chem. Abst. 94(16) 126155b) teaches the use of another complex hydrogel product to adsorb uranium from sea water. The hydrogel product was obtained by reacting titanium chloride with polyacrylic acid hydrazide (PAH). PAH is also used as a binder for an activated carbon-titanium oxide composite adsorbent to extract uranium from sea water. See, for example, S. Katoh, et al. Shikoku Kogyo Gijutsu over Shikensho Hokoku 19(2) 62-6, 1989 (Chem. Abst 109[6]41252W). After reviewing this art, one would not expect that these complex material could be substituted by a simpler hydrogel.